Molecular genetics & Clinical genetics - Special cases
Dr. Carling, Editorial note: Do not start reading about pheochromocytomas and paragangliomas here. These are rare conditions, and the likelihood that you have what is known as a “Inherited Genetic Tumor-Susceptibility Syndrome or familial pheochromocytoma & paraganglioma syndrome” is very low. However, special genetic cases of pheochromocytoma & paraganglioma syndrome do occur, and as the founder and director of the Yale Endocrine Neoplasia Laboratory, I have personally focused my scientific efforts on this area. So, I know about these rare diseases, how they can be diagnosed, managed, and treated. Also, importantly, nowadays, genetic testing is widely available, but again underutilized because of lack of knowledge, and occasional fear. However, genetic testing, if positive can make us treat tumors and cure them in the patients, but also their children and other family members, even before they occur, and a negative test can bring enormous relief and save the patient and family members unnecessary and costly imaging scans and tests.
Pheochromocytomas and Paragangliomas Risk assessment and management Disease-Specific Epidemiology
Dr. Carling Editorial note: Some of this information is technical, even for an advanced clinical endocrinologists and clinical geneticist. However, we found it important to include it, as many referring doctors and patients may benefit from understanding this information. Remember, Dr Carling is not only the best adrenal surgeon in the world but also the superior cutting-edge scientist when it comes to adrenal tumor disease.
The incidence of pheochromocytomas and paragangliomas in the general population is about 0.6 cases/100,000 per year. Historical teaching has been that 10% of pheochromocytomas and paragangliomas are hereditary, but with the discovery of pheochromocytomas and paragangliomas syndromes caused by mutations in SDHx, TMEM127, and MAX genes, it is now thought that at least 25% of pheochromocytomas and an even higher percentage of paragangliomas can be attributed to a hereditary syndrome. The risk of malignancy (cancerous pheochromocytoma or paraganglioma) varies based on the study and ranges from 2-23%. Most metastatic pheochromocytomas and paragangliomas are functional and cause catecholamine excess (adrenaline hormone production). The reported mortality rates for metastatic pheochromocytomas and paragangliomas also vary, but overall 5-year mortality is 50-60%. A total of 10 pheochromocytoma susceptibility genes have been identified to date: RET, VHL, NF1, SDHA, SDHAF2, SDHB, SDHC, SDCD, TMEM127 and MAX. Germline mutations in one of these 10 genes have been found in most hereditary cases and 10-20% of sporadic cases. Of note, MEN1 syndrome has also been very rarely associated with pheochromocytoma but is more typically linked to adrenocortical tumors.
In addition to germline mutations in the pheochromocytoma susceptibility genes, many somatic mutations have been discovered in sporadic pheochromocytoma. All pheochromocytomas and paragangliomas -associated genes discovered to date can be grouped into 3 clusters. These clusters are thought to represent distinct pathways of pheochromocytoma tumorigenesis.
• Cluster 1, known as the “pseudohypoxia subtype”, consists of genes related to cell metabolism and the hypoxia response and includes the SDHx and VHL genes. The SDHx genes encode for subunits of the succinate dehydrogenase (SDH) complex (SDHA, SDHB, SDHC, SDHD) and an assembly factor, SDHAF2. SDH and VHL both play roles in the ubiquitination and destruction process of hypoxia-inducible factor (HIF). Defects in either protein can lead to constitutive activation of the hypoxia-angiogenesis pathway. Somatic mutations in FH (fumarate hydrogenase) and EPAS1/HIF2A genes, which are involved in the hypoxia response, occur in some sporadic pheochromocytomas and paragangliomas.
• Cluster 2 represents dysregulation of kinase signaling pathways. This cluster includes the RET, NF1, TMEM127, and MAX genes. RET and NF1 are well-known players in tumorigenesis and are involved in multiple cell signaling pathways that regulate cell differentiation, survival and proliferation. MAX is a transcription factor recently identified as a pheochromocytoma and paraganglioma susceptibility gene through whole-genome sequencing. TMEM127 was discovered through linkage studies, transcription expression profiling and copy-number mapping and encodes a transmembrane protein that is thought to regulate protein trafficking and the mTOR pathway. Somatic mutations that are included in this cluster include H-RAS and ATRX mutations found in some sporadic pheochromocytoma and paraganglioma
• Cluster 3 is the Wnt signaling group and is represented by somatic mutations in the gene CSDE1 and fusions involving the gene MAML3. Mutations in CSDE1 leads to down-regulation of apoptosis while MAML3 gene mutations are associated with hypomethylation, β-catenin overexpression and Wnt signaling upregulation. Cluster 3 appears to be associated with more aggressive disease and poorer prognosis. Germline mutations have not been identified thus far in this cluster.
Hereditary pheochromocytoma and paraganglioma phenotypes are correlated with the causative germline gene mutation. The pheochromocytomas of MEN2, for example, are nearly always adrenal in location, often bilateral, and carries a low risk of metastasis. Pheochromocytoma and paraganglioma in VHL also tend to be benign but are associated with other tumors such as retinal angiomas, CNS hemangioblastomas, renal cell carcinoma and pancreatic neuroendocrine tumors. On the other hand, SDHD mutations are associated with head and neck paraganglioma, and SDHB mutated pheochromocytoma and paraganglioma have a high risk of malignancy.
Disease-Specific Approach to Risk Assessment, Counseling, and Testing
Any patient diagnosed with pheochromocytoma and paraganglioma should be evaluated for an inherited syndrome given the high prevalence of hereditary pheochromocytoma and paraganglioma. Pheochromocytoma and paraganglioma are more often associated with an inherited disorder than other adrenal tumors. Early onset of disease, multiple synchronous tumors, recurrence, metastases, and positive family history are strongly suggestive of a hereditary syndrome.
Detailed personal and family history taking should focus on the presence of syndrome-associated features such as history of medullary thyroid cancer and hyperparathyroidism (MEN2); history of CNS hemangioblastomas and renal cell carcinomas (VHL), and history of GIST, papillary thyroid cancer, pituitary adenomas, and other neuroendocrine tumors (hereditary pheochromocytoma/paraganglioma syndromes). Suspicion for a specific syndrome may be increased or decreased based on the presence of these associated features, and genetic testing can be targeted accordingly. Mutations in RET and VHL can be detected by single-gene testing. Testing for neurofibromatosis 1 typically involves chromosomal microarray analysis. Genetic testing for hereditary pheochromocytoma and paraganglioma syndromes can be performed with multigene panels that include all the known causative genes (SDHA, SDHAF2, SDHB, SDHC, SDCD, TMEM127, MAX).
Hereditary Cancer Syndromes
MEN2 patients have about a 50% chance for developing pheochromocytoma; the exact risk correlates with the location of their RET mutation, those involving codon 634 appear to have the highest risk. Pheochromocytomas in MEN2 are almost always limited to the adrenal glands, often bilateral, and rarely malignant. MEN2B is most often diagnosed in childhood due to the early onset of MTC, but 13-27% of MEN2A patients present with pheochromocytoma and paraganglioma as the initial diagnosis. It is important to identify this group of patients as they may benefit from prophylactic thyroidectomy and/or medullary thyroid cancer screening. (See MEN2 under Medullary Thyroid Cancer)
VHL is caused by pathogenic mutations in the VHL gene and is inherited in an autosomal dominant manner. About 20% of cases are caused by de novo mutations. In addition to pheochromocytoma and paraganglioma, patients with VHL are predisposed to developing retinal angiomas, CNS hemangioblastomas, renal clear cell carcinoma and cysts, endolymphatic sac tumors, and other neuroendocrine tumors. The life-time risk of developing pheochromocytoma and paraganglioma in VHL is 10-25%, and they are generally benign. There are two major sub-types of VHL: type I and type II. VHL type I is associated with truncating mutations and deletions of exons or the entire VHL gene. It carries a high risk for retinal angiomas and CNS hemangioblastomas but a relatively low risk for pheochromocytoma and paraganglioma. VHL type II is associated with missense variants and carries a relatively high risk for pheochromocytoma and paraganglioma.
Neurofibromatosis 1 is a genetic disorder commonly associated with café-au-lait spots, cutaneous neurofibromas, Lisch nodules, CNS gliomas and peripheral nerve sheath tumors. It is caused by loss-of-function mutations of the NF1 tumor suppressor gene. While pheochromocytoma and paraganglioma is not a typical tumor of neurofibromatosis 1 syndrome, 0.1-5.7% of patients with NF1 will develop pheochromocytoma and paraganglioma, a frequency that is higher than that of the general population. Up to 12% of pheochromocytoma and paraganglioma in NF1 are malignant. Interestingly, many sporadic pheochromocytoma and paraganglioma have been found to have somatic NF1 gene mutations, supporting the hypothesis that the NF1 gene does play a role in pheochromocytoma and paraganglioma tumorigenesis.
Hereditary pheochromocytoma and paraganglioma syndromes
Hereditary pheochromocytoma and paraganglioma syndromes are a group of disorders caused by germline mutations in the SDHx, TMEM127, and MAX genes that predisposes to development of pheochromocytoma and paraganglioma as well as certain other tumors such as gastrointestinal stromal tumors (GIST), renal cell carcinoma (RCC), and possibly thyroid and pituitary tumors in some cases. Most mutations are inherited in an autosomal dominant manner except for MAX, SDHAF2, and SDHD, which may have a parent-of-origin effect and appear to only be paternally inherited pheochromocytoma and paraganglioma in the head, neck, and thorax. Tumors are often benign and rarely bilateral. There appears to be an association with gastrointestinal stromal tumors (GIST) and SDHA mutations as well. SDHB pathogenic variants are associated with the highest risk for malignancy. Patients with SDHB mutations can develop pheochromocytoma and paraganglioma and often have multiple and bilateral tumors. Up to 50% of patients with metastatic pheochromocytoma and paraganglioma have a germline mutation of SDHB. In addition, patients have a higher risk of developing renal tumors including renal clear cell carcinoma, GIST, papillary thyroid cancer, and pituitary adenomas. SDHC pathogenic variants display a phenotype like SDHAF2 variants and are mainly associated with head and neck pheochromocytoma and paragangliomas. However, thoracic pheochromocytoma and paraganglioma do occur up to 10% of the time. Patients may also be at increased risk for developing GIST SDHD pathogenic variants are most frequently associated with head and neck pheochromocytoma and paraganglioma. Pheochromocytoma and paraganglioma may also occur as well as pheochromocytoma and paraganglioma in other locations. They are also associated with GIST, RCC, pituitary and thyroid tumors. SDHAF2 pathogenic variants have only been associated with benign head and neck pheochromocytoma and paraganglioma. They do not appear to carry a risk for other tumors. TMEM127 pathogenic variants are associated with pheochromocytoma and paraganglioma and may also increase the risk of renal cell carcinoma. MAX pathogenic variants are associated pheochromocytoma and more rarely paraganglioma.
How do you care for patients at increased Risk due to genetic tumor susceptibility?
Patients with MEN2 should undergo screening for pheochromocytoma, MTC and hyperparathyroidism based on ATA recommendations. Patients in the highest-risk and high-risk categories should have yearly biochemical screening for pheochromocytoma beginning at age 11. Patients in the moderate risk category should have yearly biochemical screening for pheochromocytoma beginning at age 16. (See MEN2 under Medullary Thyroid Cancer)
Von Hippel-Lindau (VHL)
Several groups have proposed recommendations for tumor screening in VHL. Most advocate for annual history and physical examination including blood pressure and neurologic evaluation, eye and retinal exams every 1-2 years, annual plasma free metanephrines, audiology evaluation every 2-3 years, brain MRI every 1-2 years, and annual abdominal ultrasound or CT/MRI. The age at which to start screening is also debated with most recommending retinal exams beginning starting from birth-2 years, pheochromocytoma screening starting from age 2, audiology exams starting from age 5, brain imaging starting from age 8, and abdominal imaging starting from age 10.
There are no recommended screening algorithms for patients with neurofibromatosis 1. Clinicians should be aware of the higher prevalence of pheochromocytoma and paraganglioma syndromes in NF1. Pheochromocytoma and paraganglioma syndromes should be suspected based on clinical signs and symptoms, and testing proceeds according to the usual practice of plasma free metanephrines and/or 24-hour urine catecholamines.
Hereditary pheochromocytoma and paraganglioma syndromes syndromes
There are no consensus recommendations regarding management and screening of patients with SDHx, TMEM127, and MAX gene mutations. It is reasonable to perform screening with annual history and physical examination, blood pressure measurement, plasma free metanephrines or 24-hour urine fractionated metanephrines, and cross-sectional whole-body imaging every 1-2 years. Pediatric patients should be started on life-long surveillance after age age 6-8. MRI can be used for pediatric or pregnant patients to minimize radiation exposure. Routine surveillance for GIST has not been recommended, but patients with unexplained gastrointestinal symptoms should undergo evaluation for a GIST.